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Normally good plugins are translation-ready, and you should create your translation files for that plugins (if not already present). Explain how to is too much for this answer, start looking at Codex page linked above, search Google and also have a look here.

If a plugin is not translation-ready use another plugin or modify it to be translation ready.

The plugins you mentioned (wp-pagenavi, Breadcrumb NavXT) are not only translation-ready but also already translated in different languages (german included), so if you have edited them, replace the original, and using WPML and they'll "magically" work without to do anything.

I can see only user interface translated for those plugins(different langs in admin), but when we are talking about custom fields, they stay still the same, no matter in what language I am browsing thru website. Any ideas, or concrete code snippet (or instructions)? :)
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VitalMar 11 '14 at 15:22